car mileage
The amount paid by one railroad for the use of cars of another railroad.
car mileage: rental fees for using another railroad's freight cars
Car mileage is the per-mile charge that one railroad pays to another for the use of its freight cars on the paying railroad's track. When a shipper books a carload that requires routing through multiple rail networks, the operating railroad compensates the car owner based on distance traveled. This system evolved because most freight movements cross multiple carrier jurisdictions, and financial settlement between carriers has been essential to the industry's functioning since the 19th century.
The rate structure historically worked as follows: a per-mile fee (quoted in cents per car-mile) is multiplied by the actual miles the car travels under the foreign railroad's operation. These rates vary by car type, condition, and era of manufacture. A loaded boxcar in good repair commands higher mileage than an aging flat car. Industry divisions between Eastern, Western, and Southeastern carriers maintained separate regional mileage schedules, though these distinctions have blurred with consolidation.
Mechanics and Accounting
Railroads track car movements through waybill data and through-service agreements. The car owner bills the operating railroad monthly or quarterly for mileage accumulated. Demurrage and per diem charges overlap with mileage fees but address different costs: demurrage covers detention time at loading or unloading facilities, while car mileage compensates for the wear of wheels, bearings, and couplings incurred through movement. A 60-foot boxcar might accumulate 100 to 200 miles per week during peak shipping seasons.
The term reflects a fundamental principle in railroad economics: the car itself is capital equipment that deteriorates with use, and that deterioration has a quantifiable cost borne by whoever owns the car. Mileage rates therefore serve as a proxy for wear, though they do not vary with load weight or speed. Modern intermodal equipment (containers on flat cars) operates under different compensation schemes, but traditional freight car mileage remains the standard settlement mechanism for general merchandise service.